<%@page contentType="text/html;charset=utf-8" %>

<%
  request.setAttribute("username","username");
%>

<%--取出数据并输出--%>
<%=request.getAttribute("username")%><br/>
${username}<br/>

<%=request.getAttribute("usernam")%><br/>
<%--EL表达式对null做了处理,如果是null，在浏览器上输出空白--%>
<%--等价于java代码 <%=request.getAttribute("usernam")%>==null?<%=request.getAttribute("usernam")%>:""--%>
${usernam}<br/>
